A plasma display panel (hereafter briefly referred to as a “panel”) is a typical image display device in which many pixels are aligned in plane, and many discharge cells including scan electrode, sustain electrode, and data electrode are formed in the panel. Gas discharge that takes place inside each discharge cell excites phosphor to emit light for color display.
In a plasma display device employing this type of panel, a subfield method is mostly adopted for displaying images. In this method, one field consists of a plurality of subfields to which predetermined luminance weight is given, respectively. An image is displayed by controlling emission and non-emission of light from each discharge cell for each subfield.
The plasma display device includes a scan electrode drive circuit for driving scan electrodes, a sustain electrode drive circuit for driving sustain electrodes, and a data electrode drive circuit for driving data electrodes. The drive circuit of each electrode applies a drive voltage waveform needed for each electrode. With respect to the data electrode drive circuit, an address pulse for independent address operation in each of many data electrode needs to be applied, based on an image signal, and thus the data electrode drive circuit is normally configured with an exclusive IC. Looking at the panel from the data electrode drive circuit, each data electrode is a capacitive load having stray capacitance between the data electrode and adjacent data electrode, scan electrode, or sustain electrode. Accordingly, this capacitance needs to be charged or discharged in order to apply a drive voltage waveform to each data electrode. For this purpose, power supply is necessary. However, to configure a drive circuit with IC, power consumption in the data electrode drive circuit needs to be suppressed as much as possible.
The power consumption in the data electrode drive circuit increases as discharging and charging current of the capacitance of data electrode increases. This discharging and charging current largely depends on an image signal to be displayed. For example, if no address pulse is applied to all data electrodes, the discharging and charging current is 0, and thus the power consumption becomes minimum. Contrarily, if an address pulse is applied to all data electrodes, the discharging and charging current also becomes 0. Accordingly, the power consumption is small. However, if the address pulse is applied to data electrodes at random, the discharging and charging current increases. In particular, if the address pulse is applied alternately to adjacent data electrodes, static capacitance between the adjacent data electrodes, and static capacitance between the scan electrode and sustain electrode will be discharged and charged. This results in extremely large power consumption.
One proposed method of reducing power consumption in the data electrode drive circuit is to restrict power consumption in the data electrode drive circuit by calculating power consumption in the data electrode drive circuit based on the image signal, and prohibiting the address operation sequentially from a subfield with the smallest luminance weight if power consumption is large. (For example, refer to Patent Document 1.) Alternatively, another method disclosed is to reduce power consumption in the data electrode drive circuit by replacing an image signal with an image signal that reduces power consumption in the data electrode drive circuit. (For example, refer to Patent Document 2.)
To reduce the power consumption in the data electrode drive circuit, a circuit for detecting or calculating the power consumption in the data electrode drive circuit and a circuit for reducing the power consumption in the data electrode drive circuit are provided, and the power consumption in the data electrode drive circuit is controlled to be below a predetermined power threshold. Control types include feedback and feed-forward. To ensure suppression of the power consumption below the predetermined power threshold, the feedback control is relatively simple and effective. However, a simple feedback control results in repetitive increase and decrease of the power consumption in the data electrode drive circuit around the predetermined power threshold. This results in flickering. To prevent oscillation due to the feedback control, the power threshold when the power consumption increases is set greater than the power threshold when the power consumption decreases so as to give hysteresis characteristics to the control. However, since the increase and decrease of power consumption largely depends on image signal, it is practically difficult to set two appropriate predetermined power thresholds.    Patent Document 1: Japanese Patent Unexamined Publication No. 2000-66638    Patent Document 2: Japanese Patent Unexamined Publication No. 2002-149109